1. Technical Field
The present invention relates generally to waterjet systems and, in particular, to abrasive jet systems capable of producing multi-abrasive jets.
2. Description of the Related Art
Conventional waterjet systems are used to process workpieces by pressurizing fluid and then delivering the pressurized fluid against a workpiece. An abrasive jet system is a type of waterjet system that produces a high-pressure abrasive jet suitable for cutting through relatively hard materials. Abrasive jet systems often have a jewel orifice in a cutting head assembly. High-pressure fluid flows through the jewel orifice to form a high-pressure fluid jet inside of the cutting head assembly. Abrasive is entrained in the fluid jet to produce an abrasive jet. The abrasive jet passes through a mixing tube retained by a cutting head body and is ultimately discharged towards the workpiece.
Garnet abrasive is commonly used to produce abrasive jets suitable for cutting a wide range of different materials while producing a minimal amount of wear along the mixing tube. Unfortunately, cutting rates achieved utilizing garnet abrasive may be relatively low, especially when cutting workpieces made of hard, wear-resistant materials, such as ceramics (e.g., alumina ceramic, zirconia, etc.), ceramic matrix composites, carbides (e.g., tungsten carbide, titanium carbide, and the like), sapphire, and other materials capable of withstanding exposure to abrasive jets, such as materials often used to make armor (e.g., armor for military vehicles, body armor, etc.). Even though garnet abrasive has a low material cost, it may result in an expensive, time consuming manufacturing process, especially if used to cut these hard, wear-resistant materials, thus rendering it unsuitable for cost-effective processing.
Relatively hard abrasive, such as aluminum oxide, can be used to cut hard, wear-resistant materials at relatively high cutting speeds. Unfortunately, hard abrasives often have a high material cost and produce high wear rates of the mixing tube that result in frequent mixing tube replacement. When an abrasive jet carrying only hard abrasive passes through the mixing tube at a high velocity, the mixing tube, even if made of a wear-resistant material, experiences appreciable wear. Mixing tubes have to be replaced periodically within a time as short as a half hour, or perhaps as long as 100 hours, depending upon the material forming the mixing tube, as well as other factors, such as the hardnesses of entrained abrasive, working pressures, flow rates, manufacturing tolerances, etc. Frequent replacement of worn mixing tubes often leads to problems, such as damage to the cutting head body, misalignment of the mixing tube, machine downtime, and the like. Accordingly, hard abrasive is unsuitable for cost-effective processing. Also, increasing the working pressure of the fluid used to make the abrasive jet may not significantly increase cutting rates of many types of hard materials.